The objective of the proposed research is to investigate the mechanisms of regulation of parathyroid hormone (PTH) biosynthesis, secretion, and metabolism and the activation of vitamin D. The methods to be employed include superfusion of parathyroid tissue in vitro, measurement of calcium transport in parathyroid tissue in vitro, determination of calcium binding protein (CaBP) concentrations in normal, abnormal and experimentally altered parathyroid tissue, amino acid incorporation into PTH and CaBP in vitro, the calcium-regulated conversion of PTH in vitro and PTH metabolism in vivo, and a study of the hydroxylations of vitamin D and 25-hydroxycholecalciferol in liver and kidney mitochondria.